Concentration can be of great value, but it can also be seriously limiting if you become seduced by the pleasant quality of this inner experience and come to see it as a refuge from life in an unpleasant and unsatisfactory world. You might be tempted to avoid the messiness of daily living for the tranquility of stillness and peacefulness. This of course would be an attachment to stillness, and like any strong attachment, it leads to delusion. It arrests development and short-circuits the cultivation of wisdom.